Few wildlife topics are as enthusiastically debated as the whereabouts of deer, which can be elusive even if nearby. This is particularly true when firearms season begins, when many whitetails, bucks in particular, move exclusively at night to avoid ending up in someone's cross hairs.
Hunters pursuing these now-you-see-'em-now-you-don't deer might reasonably conclude no whitetails exist in their areas, or if there were deer nearby, they'd moved on. In most cases the hunters would be mistaken. Deer, like people, do what's necessary to avoid danger. More often than not, this means hiding rather than fleeing.
The whereabouts of deer can similarly stymie wildlife biologists. In days gone by these professionals would count droppings along given routes to help determine an area's whitetail population. Though labor intensive, this provided a fairly reliable deer population index. Today, deer populations are "modeled" using computer software programs that integrate multiple pieces of information, especially past seasons' harvest results.
Still, biologists, like hunters, often wonder if they're missing something while estimating whitetail numbers. In an attempt to "ground truth" their population estimates, Minnesota Department of Natural Resources whitetail biologists until recently flew over various deer permit areas. This method provided accurate census information, but was expensive and too dependent on safe flying weather and other variables.
Enter now the drone, whose usefulness has only recently been realized in determining deer and other wildlife populations, said Eric Michel, DNR farmland deer project leader stationed in Madelia, Minn.
As the DNR researcher who helps determine whitetail population estimates for the state's 130 Deer Permit Areas, Michel thinks a lot — perhaps continually — about "just how many deer are out there."
Critical to making such estimates, he said, is accurately assessing the number of fawns born in Minnesota's various regions and determining their rates of survival to breeding age.
"Fawn survival is an important component of determining deer populations," Michel said. "Here in the southwest part of the state, we're just beginning a three-year fawn survival study using drones to help us find fawns shortly after they're born so we can get to them and outfit them with GPS transmitting collars."
The study area chosen by Michel and a colleague, DNR wildlife research biologist Tyler Obermoller, spans some 2,800 square miles in south-central Minnesota and includes Deer Permit Areas 252, 253, 296 and 299.
"Before drones became an option, locating fawns was inefficient and expensive," Michel said. "The old method required us to capture does and sedate them to insert a transmitter in them that sensed the temperature change that occurs when a doe gives birth to a fawn. When we received this signal, we had to hurry in and find the fawn and put a collar on her."
Using a drone to locate fawns shortly after they're born is far more efficient and less expensive, Michel said.
Flown as early as 2 a.m. by a DNR contractor from the Twin Cities, the drone in Michel's study will follow preprogrammed routes over state wildlife management areas within the research area. An infrared camera attached to the drone will search for the heat-produced "signature" of a freshly born fawn that usually is accompanied by a similar signature of the nearby mother.
"Fawns have almost no scent, which is how they avoid predators," Michel said. "So the mother will leave her fawn where it lies and move away so predators can't scent her and get to her fawn."
When a drone locates a fawn, the animal's longitude and latitude are recorded. The drone returns in daylight to confirm the animal's location and photograph it using a second, color camera. Then a crew of two or three researchers hikes to the location to weigh and record other information and fit the fawn with a transmitter collar.
"A doe generally will return to her fawn and move it every three or four hours to avoid detection by predators," Michel said. "When the mother returns, it will stimulate the fawn to defecate, so the young deer leaves its scent in its old location, before moving to a new spot."
In Minnesota farmlands, coyotes are the major fawn predator. Twenty years ago, when the most recent fawn survival study was conducted in the southwest, coyote numbers were believed to be down due to a disease, which might have artificially inflated the region's fawn survival estimates, Michel said.
"The collars we are using will last up to 18 months and will send data to us every four to six hours," he said. "In addition to fawn survival, we want to know when the fawns disperse from their mothers and how they use the landscape.
'We hope to conduct similar studies in the state's forested regions so we can have the most accurate information possible to determine deer populations."